Self-processing photographic film units are now available which are completely self-contained and are adapted to be employed in a camera in which the film unit is exposed and then processed by moving it between a pair of pressure-applying members. The components of the film unit are assembled to form an integral structure and the integrity of this structure is maintained during exposure, processing and viewing, thereby making it unnecessary to store, handle and/or move separately, individual elements of the film unit, and minimizing the complexity of the structure required to contain and manipulate the film unit to effect exposure and processing thereof. Such a film unit structure is attractive, includes a minimum of simple and easily assembled components, is of a minimum size in relation to image size and generally includes substantially no excess materials. The film unit includes a container of the processing fluid and means for promoting and facilitating spreading of the fluid in a layer of predetermined depth and extent.
Such film units generally comprise two separate, flexible sheetlike elements including a first or image-recording sheet including a layer containing a photosensitive image-recording material and a second sheet for aiding in the distribution of a viscous liquid processing agent as a layer in contact with an exposed area of the photosensitive material. A rupturable container filled with a fluent processing composition, is disposed along one edge of the film unit, in a manner well known in the art. After the viscous fluent processing composition has been spread from the leading end of the film unit between the sheets toward the trailing end thereof, excess processing fluid is trapped and retained within the film unit at the trailing end thereof.
In prior art film units of the general type described above, various means have been provided for forming a trapping volume or receiver at the edge of the film unit. Examples of such trap structures are illustrated in U.S. Pat. Nos. 3,589,904, 3,607,285, 3,619,193, 3,621,768, 3,689,269, 3,741,766 and 3,776,732. The trap structures of the U.S. Pat. Nos. 3,589,904, 3,621,768 and 3,741,766 patents all utilize spacer members, which space apart the pressure members in the trap area to permit the retention of the excess processing composition. These spacer members are formed from separate elements that must be handled by the assembly apparatus and be located in the individual film units within close tolerances. Moreover, each of the spacer members themselves occupy a significant amount of the trapping volume that might otherwise hold a portion of the excess composition. Thus, either the volume of excess processing composition that can be accommodated must be limited or the size of the trap must be enlarged.
The trap structures of the U.S. Pat. Nos. 3,589,904, 3,619,193, 3,689,269 and 3,776,732 patents utilize a portion of the end of one of the film unit sheets which is embossed to provide the spacing function of the spacer members noted above. However, the trap construction of these patents only utilize one surface of the embossed sheet whereby the potential trapping space is reduced by the embossed portions of the sheets.
With each of the foregoing trap constructions, except for the U.S. Pat. No. 3,607,285, it is possible for the excess processing composition in the trap to be forced, after spread, back into the image area to discolor or otherwise impair the visible image. The U.S. Pat. No. 3,607,285 illustrates an after-process seal between the trap and the image area that is intended to prevent such back flow. However, it has been found that such an after-process seal complicates the manufacture of the film unit and that it does not function sufficiently reliably to warrant its use.